CHICAGO, IL, USA (UroToday.com) - Shockwave lithotripsy (SWL) is a common primary method of treatment for most renal calculi. Success rates are varied and depend on both patient and stone related factors. To date, there are no algorithms which accurately predict the success of SWL.
Dr. Ray and colleagues from the University of Toronto, Ontario, Canada performed a retrospective analysis to develop a pre-treatment nomogram to predict SWL outcome. Eligible patients had a non-contrast CT scan within 72 days of treatment demonstrating a solitary renal calculus ≤2 cm and returned for follow up. Follow up was conducted at 2 weeks and 3 months after treatment using CT and KUB imaging. Success was defined as either being stone free or having ≤4 mm residual fragments after a single SWL treatment. 144 patients were analyzed with the following factors found to be predictive of success on univariate analysis: stone attenuation <1000 Hounsfield Units, skin-to-stone distance <105 mm, stone area <100mm2, maximal stone length on KUB and CT, BMI, and stone location. Multivariate analysis showed only stone size and skin-to-stone distance as significant predictors of SWL outcome (p<0.003). Age, gender, side, presence of hydronephrosis or presence of a stent did not predict outcome. Patients with favorable outcome predictors such as small area, short skin-to-stone distance, and low attenuation on CT had a success rate of 84.4% vs 33.3% for unfavorable predictors for all three (p<0.001).
Despite the release of guidelines by the EUA and AUA for nephrolithiasis, many urologists continue to use SWL in situations where stone free rates are dismal. A validated algorithm may provide standard guidance for the practice of SWL treatment and improve patient stone free rates and decrease retreatment rates.
Presented by A.Andrew Ray, MD, et al. at the Annual Meeting of the American Urological Association (AUA) - April 25 - 30, 2009 - McCormick Place Convention Center - Chicago, Illinois, USA.